The present invention relates generally to integrated circuit chip package technology, and more particularly to a unique lead frame design for a micro lead frame (MLF) package adapted to improve the longevity of the cutting blades used in a saw isolation and/or saw singulation process employed during the manufacture of the MLF package.
Integrated circuit dies are conventionally enclosed in plastic packages that provide protection from hostile environments and enable electrical interconnection between the integrated circuit die and an underlying substrate such as a printed circuit board (PCB). The elements of such a package include a metal lead frame, an integrated circuit die, bonding material to attach the integrated circuit die to the lead frame, bond wires which electrically connect pads on the integrated circuit die to individual leads of the lead frame, and a hard plastic encapsulant material which covers the other components and forms the exterior of the package.
The lead frame is the central supporting structure of such a package. A portion of the lead frame is internal to the package, i.e., completely surrounded by the plastic encapsulant. Portions of the leads of the lead frame extend externally from the package or are partially exposed within the encapsulant material for use in electrically connecting the chip package to another component. In certain chip packages, a portion of the die pad of the lead frame also remains exposed within the exterior of the package for use as a heat sink.
For purposes of high-volume, low-cost production of chip packages, a current industry practice is to etch or stamp a thin sheet of metal material to form a panel or strip which defines multiple lead frames. A single strip may be formed to include multiple arrays, with each such array including a multiplicity of lead frames in a particular pattern. In a typical chip package manufacturing process, the integrated circuit dies are mounted and wire bonded to respective ones of the lead frames, with the encapsulant material then being applied to the strip so as to encapsulate the integrated circuit dies, bond wires, and portions of each of the lead frames in the above-described manner.
Upon the hardening of the encapsulant material, the lead frames within the strip are cut apart or singulated for purposes of producing the individual chip packages. Such singulation is typically accomplished via a saw singulation process. In this process, a saw blade is advanced along “saw streets” which extend in prescribed patterns between the lead frames as required to facilitate the separation of the lead frames from each other in the required manner.
One of the drawbacks associated with current, conventional lead frame design and, hence, the configuration of the strips defining multiple such lead frames is that the saw blade used in the saw singulation process cuts through copper (i.e., the metal material typically used to fabricate the strip) approximately ninety percent of the time. As will be recognized, this level of sawing through copper as occurs as a result of the configuration of the strip often results in the premature wear of the costly saw singulation blades. The present invention addresses this drawback by providing a unique lead frame design for an MLF package which is adapted to improve the longevity of the cutting blades used in the saw singulation process involved in the manufacture of the MLF package. More particularly, in the present invention, the amount of copper included in the lead frames and, hence, the strip is reduced, particularly in the cutting areas. The copper reduction is designed in, and facilitated during the etching process employed during the manufacture of the strip. The configuration of the lead frame and thus the strip effectively reduces blade contact with copper by approximately eighty percent, thus providing a substantial cost benefit by reducing premature blade wear and providing a lower cost MLF package. These, and other advantages of the present invention, will be discussed in more detail below.